“The findings are disturbing, because they’re a reversal of a long-standing trend,” Idler says.

The suicide rate for the U.S. population overall has been declining for decades, Idler notes. And people aged 40-59, in particular, have long had a moderate suicide rate.

The baby boomers, people born between 1945 and 1964, have broken that pattern. By 2000, most people aged 40 to 59 were baby boomers and the suicide rate started climbing steadily for these middle-age ranges. The authors found significant increases of more than 2 percent per year for men, and more than 3 percent per year for women, from 1999 to 2005. (By 2005, all middle-aged people were baby boomers.)

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The post-1999 increase has been particularly dramatic for those who are unmarried and those without a college degree, the analysis showed. For example, from 2000 to 2005, the suicide rate jumped nearly 30 percent for men and women aged 50 to 59 with some college but no degree. Middle-aged people with a college degree appeared largely protected from the trend.

The baby boomers also experienced higher suicide rates during their adolescence and young adulthood, doubling the rate for those age groups at the time. Their suicide rate then declined slightly and stabilized, before beginning to increase again in midlife.

“You might think that the higher rates in adolescence would lead to lower rates later because the most suicide prone people would be gone but that doesn’t appear to be the case,” Idler says. “Clinical studies often show that knowing someone who committed suicide is considered a risk factor for later doing it yourself, and that may be one factor here. The high rates in adolescence could actually be contributing to the high rates in middle age.”

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Higher rates of substance abuse and the onset of chronic diseases are among other possible factors in the rising baby boomer suicide rate. “As children, the baby boomers were the healthiest cohort that had ever lived, due to the availability of antibiotics and vaccines,” Idler says. “Chronic conditions could be more of a rude awakening for them in midlife than they were for earlier generations.”

Traditionally, midlife has been considered a time when people are at their peak of social integration. “We need to pay attention to this new increase in suicides, during a period of life previously thought to be stable and relatively protected from suicide, and in an age group now occupied by extraordinarily large numbers of people,” Idler says.

Data for the study were drawn from the National Center for Health Statistics and the U.S. Census Bureau. Preliminary data from 2006 and 2007, the latest time that statistics are available, indicate that the upward pattern in midlife suicide is continuing, Idler says.